The present invention relates to an output circuit and output circuit device for driving a laser diode or the like at high speed.
A conventional output circuit for supplying a drive signal to a laser diode or the like at high speed comprises an emitter follower circuit and a differential circuit. The emitter follower circuit receives a differential signal input to the output circuit device. The differential circuit is driven by a signal output by the emitter follower. In the device, the power supply for the emitter follower circuit is located near the emitter follower transistor.
The output transistor incorporated in the output circuit device must be a large-size one so that the device may convert a high-frequency signal into a large output current. The large the output transistor, the greater its ground parasitic capacity. Ringing inevitably occurs when the output transistor operates at high speed. Hence, the differential transistors incorporated in the device may oscillate if their base terminals are electrically unstable. To remove this phenomenon, an integration circuit is used to abate the waveform sharpness of the signal input to the differential transistors. As a consequence, the output circuit device cannot supply a drive signal at high speed.